In order to analyze liquid samples one often requires an apparatus which enables initially filtration of the samples, then metering thereof. Such an apparatus may be used for instance in the measurement of the ATP (adenosine triphosphate) content of a substance in order to be able to estimate the biological activity thereof
In an article of the review "Soil Biol. Biochem." volume 16, Nr 4, pages 361-366, 1984, N. Maire describes a method of analysis of a medium such as soil which consists in extracting the ATP molecule from the cells of the medium by rupture of the cell walls, then by the photometric measurement of the molecule by an enzymatic reaction of the bioluminescence, the intensity of the emitted light in the course of this reaction being directly proportional to the concentration of ATP, this concentration itself representing the biological activity of the sample of examined soil. Effectively, ATP is a mononucleotide of metabolism which is found in all living organisms and which assures transmission or stockage of energy reserves in the majority of biochemical reactions taking place at the center of living cells (respiration, fermentation, photosynthesis, etc.).
The extraction of the ATP molecule by rupture of the cell walls is brought about by diluting the soil sample in a certain quantity of acid such as H.sub.2 SO.sub.4, preferably completed by a mechanical mixing operation of the thus diluted sample. Since furthermore, the enzymatic reaction necessary for the photometric analysis does not withstand an acid medium, it is necessary, before proceeding with the photometric analysis, to adjust the pH to an almost neutral value by addition of a special additive intended to this effect. The adjustment of the pH must naturally take place within a well determined volume of the sample and it is at this level that in the arrangement described hereafter are to be found the essential characteristics of this invention.
It is well understood that the description to follow of this analysis arrangement must not be considered as a limitation to the applications of the invention which, on the contrary, may be employed each time that one wishes to obtain filtering and metering of a certain number of individual samples without there being risk of contamination of the samples among themselves.
Effectively, when one wishes to treat successively a large number of liquid samples with a precise volumetric metering, one is confronted with a problem of rinsing the elements which provide the metering and the ducting which establishes the communication between these various elements.
Generally, the cleaning of a flow circuit of the samples is brought about with a rinsing liquid which washes them between the metering of the successive samples in order to flush all residue of the previously treated sample.
In failing to take this precaution, such residues may modify the characteristics of the following sample such as for instance its composition or its concentration, from which there may well result errors when analysis is undertaken.
Beside the fact that the rinsing operation risks modifying the concentration of the samples, since there remains always within the flow circuit a certain quantity of rinsing liquid, it is necessary likewise to observe that this operation requires special elements and that furthermore it prolongs the treatment time of each sample since during the cleaning operation metering may not take place.
U.S. Pat. No. 4,869,116 describes a method and an apparatus by means of which the metering of successive samples may be brought about without disturbing either the composition or the concentration of the samples and likewise without increasing the time necessary for treating each sample over and beyond the time interval strictly necessary for the metering operation.
In order to obtain this result, the described method consists in preparing in several first recipients samples the volume of which is made up of the quantity of sample desired plus an excess quantity of sample, and successively decanting the contents of each of the first recipients initially towards an outlet up to the amount of the excess quantity, then towards the second recipient until the desired quantity of sample has been obtained. Thus the excess quantity of the following sample is itself employed for rinsing the flow circuit, in flushing from this circuit all residue of the preceding sample, following which the second recipients may receive only a correct quantity of sample exclusively made up of the liquid formed by the following sample.
The abovementioned characteristics are found in the present invention which however proposes an improvement of the method in the sense that filtering of the sample is totally independent of its metering which thus enables a more precise metering. Furthermore, the present invention leads to the proposal of an arrangement less complicated and more universal in its employment.